We've just released Synapse 1.7.2 - a minor point release to address two regressions which snuck into 1.7.0 and 1.7.1. Sorry for the upgrade faff; hopefully we will be back to a saner release cadence shortly. Reminder that if you are on 1.7.0 or earlier you should upgrade asap as 1.7.1 contained security fixes.
Get the new release from github or any of the sources mentioned at https://github.com/matrix-org/synapse/blob/master/INSTALL.md.
The changelog since 1.7.1 is:
Synapse 1.7.2 (2019-12-20)
This release fixes some regressions introduced in Synapse 1.7.0 and 1.7.1.